A low-pass filter allows signals with frequencies lower than a cut-off frequency and attenuate signals with frequencies higher than the cut-off frequency. Often, removing noise at low frequencies is difficult unless the cut-off frequency of the low-pass filter is extremely low.
The cut-off frequency is inversely proportional to product of resistance value of a resistor and capacitance value of a capacitor of the low-pass filter. It is desired to have a large value of resistance and capacitance for generating a low cut-off frequency. Typically, the resistor is placed inside the integrated circuit and the capacitor is placed outside the integrated circuit. In an existing technique, for having a low cut off frequency, a low-pass filter having a resistor of high resistance value is included in the integrated circuit. In one example, a diode can be used in place of a resistor to provide high resistance value in the low-pass filter. However, having a high resistance value causes voltage drop across the resistor due to leakage current in the integrated circuit.
In light of the foregoing discussion, there is a need for a filter circuit having a low cut-off frequency.